1. Field of the Invention
This invention relates to a high precision positioning device, and more particularly to a high precision positioning device for a floater floatingly supported by an air bearing for parallel movement relative to a guide member.
2. Description of the Prior Art
The high precision positioning device according to the present invention is applicable to instruments in many fields which require high precision positioning in X and Y directions, but description will hereinafter be made by taking as an example the high precision positioning of an XY stage in a mask aligner or a photorepeater or the like for the production of semiconductors for which a high precision is especially required.
These years have seen remarkable advance in the tendency toward minute size and high integration of the pattern of semiconductor elements, IC, LSI or the like and the pattern line width is going to be 1 to 2 .mu.m. In promoting the minute size and high integration of the pattern, it is required to provide a printing performance which enables printing of patterns as minute as 1 to 2 .mu.m, to accurately align about ten photomask patterns over a plurality of process steps, and to accurately position the pattern printed on semiconductor wafers by the photomask of the preceding step and the pattern of the photomask.
Generally, the accuracy with which these are positioned is required to be about 1/10 of the line width, and for the line width of 1 to 2 .mu.m, the positioning accuracy of 0.1 to 0.2 .mu.m has become necessary. An XY stage which will satisfy these requirements must satisfy the following conditions:
1. Being capable of effecting position measurement which satisfies the positioning accuracy;
2. The XY stage should be smoothly guided so as to be able to respond to a fine feed; and
3. Being provided with a drive mechanism which can reliably feed the XY stage in a minute unit.
According to the prior art, condition 1 above may be satisified by a laser interferometer or the like and condition 2 above may be satisfied by an air bearing guide or the like.
The present invention has been made as an effective device which satisifies condition 3 above. Heretofore, various driving methods for highly precisely positioning the XY stage have been provided such as the driving method using a combination of a motor and a feed screw, a fine feed mechanism using a piezo element or the like.
However, effecting high precision positioning of the order of micron by the use of the combination of a motor and a feed screw has required a high degree of mechanical accuracy and on the other hand, the movement span provided by the driving method using piezo or the like is of the order of 1 to 2 .mu.m at best and moreover, to provide such a degree of movement, a voltage of several thousand volts had to be applied to a piezo element of a relatively great length, say, of the order of 30 mm.
Also, the conventional method for positioning the stage with respect to two orthogonal directions has comprised driving the XY stage along an X-direction guide to determine the position in X-direction and driving the XY stage along a Y-direction guide to determine the position in Y-direction, with the X- and Y-direction guides of the XY stage as the fixed reference.